The present invention relates to a brake circuit for an automobile, especially a cylinder apparatus used for a brake fluid pressure control system, a so-called brake-by-wire (BBW) system, for controlling a fluid pressure from a fluid pressure source and applying the fluid pressure to wheel cylinders in accordance with operation of a brake pedal.
The BBW system generally includes a fail-safe master cylinder which operates in the event of failure of the system, and also includes a stroke simulator for securing a desired stroke of the brake pedal in normal operation of the system. Generally, in conventional BBW systems, an accumulator or damper is used as the stroke simulator, wherein a volumetric change is effected according to the fluid pressure of the master cylinder. In such conventional BBW systems, not only the fluid to be supplied to the accumulator or damper, but also the fluid to be supplied to the wheel cylinders must be secured in the master cylinder, so that the master cylinder needs to be large.
As a countermeasure, for example, Unexamined Japanese Patent Application Public Disclosure (Kokai) No. 7-165031 proposes a brake control apparatus (BBW system) shown in FIG. 4 (an excerpt from Kokai No. 7-165031). In this apparatus, a pedal feeling adjusting mechanism (stroke simulator) f is provided between a brake pedal a and a master cylinder b. The pedal feeling adjusting mechanism f comprises: a first rod f1 provided on a side of the master cylinder b; a second rod f2 provided on a side of the brake pedal a; and a spring f3 provided between the first rod f1 and the second rod f2. In normal operation of the system, a desired stroke of the brake pedal a is secured by contracting the spring f3. In the event of failure of the system, for fail-safe operation, the second rod f2 abuts against the first rod f1, to thereby transmit a stepping force applied to the brake pedal a directly to the master cylinder b.
However, in the stroke simulator of Kokai No. 7-165031, when the master cylinder b operates for fail-safe operation, a driver needs to force the brake pedal a by a distance corresponding to the stroke of the master cylinder b (i.e., the stroke of a piston in the master cylinder b) in addition to a distance corresponding to the stroke consumed by the stroke simulator f in normal operation of the system. Thus, an invalid stroke of the brake pedal becomes large, so that the brake pedal a must be forced deeply and strongly as compared to normal braking, in order to achieve the same deceleration. Therefore, braking becomes extremely difficult.
In view of the above, the present invention has been made. It is an object of the present invention to provide a cylinder apparatus for a brake fluid pressure control system, which serves as a stroke simulator in normal operation of the system and which markedly suppresses an increase in invalid stroke of the brake pedal for fail-safe operation, to thereby secure a desired stroke of the brake pedal without impairing brake operability.
In order to achieve the above-mentioned object, the present invention provides a cylinder apparatus for a brake fluid pressure control system for controlling a fluid pressure from a fluid pressure source and applying the controlled fluid pressure to a wheel cylinder in accordance with operation of a brake pedal, the cylinder apparatus comprising a tandem master cylinder adapted to supply a fluid to the wheel cylinder in the event of failure of the brake fluid pressure control system.
The tandem master cylinder has a cylinder body, a primary piston and a secondary piston, each slidably provided in the cylinder body, and a primary pressure chamber defined between the primary piston and the secondary piston. In addition, the tandem master cylinder has a secondary pressure chamber defined between the secondary piston and the cylinder body, and communication preventing means which communicate the primary pressure chamber with a reservoir when an amount of stroke of the secondary piston reaches or falls below a predetermined level and which prevents the communication between the primary pressure chamber and the reservoir when the amount of stroke of the secondary piston exceeds the predetermined level.
In the cylinder apparatus of the present invention, in normal operation of the BBW system, the amount of stroke of the secondary piston is very small, so that the fluid in the primary pressure chamber is discharged to the reservoir by the communication preventing means and a return spring in the primary pressure chamber contracts, to thereby secure a desired stroke of the brake pedal. Thus, the cylinder apparatus as a whole serves as a stroke simulator. On the other hand, in the event of failure of the BBW system, for fail-safe operation, the fluid in the secondary pressure chamber is supplied to the wheel cylinders in one of the brake circuits, so that the amount of stroke of the secondary piston becomes large and therefore the communication preventing means prevents communication between the primary pressure chamber and the reservoir. This makes it possible to supply the fluid in the primary pressure chamber to the wheel cylinders in the other brake circuit. Therefore, the cylinder apparatus as a whole not only serves as a fail-safe master cylinder, but also serves as a tandem master cylinder which is effective for fail-safe operation in the event of failure of wheel braking circuits. Further, when the cylinder apparatus serves as the tandem master cylinder, contraction of the return spring in the primary pressure chamber, which spring serves as the stroke simulator in normal operation of the BBW system, can be minimized, so that the invalid stroke of the brake pedal can be minimized and good brake operability can be secured.
In the cylinder apparatus of the present invention, it is preferred that the primary piston have a larger pressure-receiving area than the secondary piston. By this arrangement, when the cylinder apparatus serves as the fail-safe master cylinder, the primary pressure chamber can be reduced in volume simply by moving the primary piston, so as to supply a desired amount of fluid to the wheel cylinders. Therefore, the amount of contraction of the return spring in the primary pressure chamber, which serves as the stroke simulator in normal operation of the BBW system, is very small, so that it is possible to avoid lowering of efficiency in fluid pressure generation due to a rise in reaction force from the spring.
The present invention also provides a cylinder apparatus adaptable to a brake fluid pressure control apparatus.
The cylinder apparatus has a cylinder body, a first piston slidably provided in the cylinder body to receive a braking force from a brake pedal, a second piston slidably provided in the cylinder body in a spaced relationship with the first piston, a first pressure chamber defined between the first piston and the second piston, and a second pressure chamber defined between the second piston and the cylinder body.
In addition, the cylinder apparatus has first biasing means provided in the first pressure chamber to bias the first piston and the second piston away from each other and capable of transmitting the braking force from the first piston to the second piston, second biasing means provided in the second pressure chamber to bias the second piston toward the first piston, a first discharge port for communicating the first pressure chamber with a first wheel cylinder, a second discharge port for communicating the second pressure chamber with a second wheel cylinder, a rear reservoir port provided on the rear side of the cylinder body to communicate with a reservoir, a front reservoir port provided on the front side of the cylinder body to communicate with the reservoir, a first passage for providing communication between the first pressure chamber and the rear reservoir port, a second passage for providing communication between the second pressure chamber and the front reservoir port, and a third passage for providing communication between the first pressure chamber and the front reservoir port.
Further, the cylinder apparatus has a device for preventing the communication through the first passage during braking, a device for preventing the communication through the second passage during braking, and a device for allowing the communication through the third passage in normal operation of the brake fluid pressure control apparatus during braking and preventing the communication through the third passage in the event of failure of the brake fluid pressure control apparatus during braking.
The present invention further provides a cylinder apparatus adaptable to a brake fluid pressure control apparatus.
The cylinder apparatus has a cylinder body, a first piston slidably provided in the cylinder body to receive a braking force from a brake pedal, a second piston slidably provided in the cylinder body in a spaced relationship with the first piston, a first pressure chamber defined between the first piston and the second piston, a second pressure chamber defined between the second piston and the cylinder body, first biasing means provided in the first pressure chamber to bias the first piston and the second piston away from each other and capable of transmitting the braking force from the first piston to the second piston, and second biasing means provided in the second pressure chamber to bias the second piston toward the first piston.
In addition, the cylinder apparatus has a first discharge port for communicating the first pressure chamber with a first wheel cylinder, a second discharge port for communicating the second pressure chamber with a second wheel cylinder, a rear reservoir port provided on the rear side of the cylinder body to communicate with a reservoir, a front reservoir port provided on the front side of the cylinder body to communicate with the reservoir, a first passage for providing communication between the first pressure chamber and the rear reservoir port, a second passage for providing communication between the second pressure chamber and the front reservoir port, and a third passage for providing communication between the first pressure chamber and the rear reservoir port.
Further, the cylinder apparatus has a device for preventing the communication through the first passage during braking, a device for preventing the communication through the second passage during braking, and a device for allowing the communication through the third passage in normal operation of the brake fluid pressure control apparatus during braking and preventing the communication through the third passage in the event of failure of the brake fluid pressure control apparatus during braking.
The present invention further provides a cylinder apparatus adaptable to a brake fluid pressure control apparatus.
The cylinder apparatus has a cylinder body, a first piston slidably provided in the cylinder body to receive a braking force from a brake pedal, a second piston slidably provided in the cylinder body in a spaced relationship with the first piston, a first pressure chamber defined between the first piston and the second piston, and a second pressure chamber defined between the second piston and the cylinder body.
In addition, the cylinder apparatus has first biasing means provided in the first pressure chamber to bias the first piston and the second piston away from each other and capable of transmitting the braking force from the first piston to the second piston, second biasing means provided in the second pressure chamber to bias the second piston toward the first piston, reservoir port means communicating with a reservoir, a first passage for providing communication between the first pressure chamber and the reservoir port means, a second passage for providing communication between the second pressure chamber and the reservoir port means, and a third passage for providing communication between the first pressure chamber and the reservoir port means.
Further, the cylinder apparatus has a device for preventing the communication through the first passage during braking, a device for preventing the communication through the second passage during braking, and a device for allowing the communication through the third passage in normal operation of the brake fluid pressure control apparatus during braking and preventing the communication through the third passage in the event of failure of the brake fluid pressure control apparatus during braking.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.